We are studying the synthesis and hydrolysis of esterified cholesterol using acetone powder of aortas. The ratio of synthesis (S) to hydrolysis (H) changes with age and cholesterol feeding. We propose to investigate the effect of hypolipidemic drugs and of diet on the cholesterol esterase activity of rabbit and rat aorta preparations. Drugs used will be the standard ones in use today (Atromid-S; D-thyroxine; cholestyramine) as well as any others which appear to be active (such as Tibric Acid, DH-990; colestipol). The diets will either be a standard atherogenic regimen (cholesterol alone or with saturated or unsaturated fat) or a semi-purified, cholesterol-free regimen. We also plan to investigate further the nature of the enzyme(s) and attempt purification and characterization. We will also study the isoenzymes of beta-N-acetylhexosaminidase in sera of normal humans and in persons with cancer or hyperlipidemia. The isozymes will also be studied in normal and transformed human diploid cells.